CONAR RECEIVER MODIFICATIONS !!!
"....a face only a mother could love."
Short Wave Broadcast mods
These mods allow the CONAR receiver reception outside Amateur bands.
So what is shortwave broadcast like on a CONAR? Acutally pretty darn good. No doubt you have maveled at the very clean audio on 80 Meters AM signals on 3.885 Megacycles. To give shortwave listening (SWL) a try - tune to the upper part of 40 meters any evening and switch the BFO to AM. Pretty good huh?
The CONAR makes a pretty good SWL receiver. It's cute enough that most ex-young ladies (XYL's) don't really mind if you bring it into the living room. With it's cosmic blue paint job, internal speaker and simple shiny face plate, the CONAR almost becomes a 60's fashion statement in it's own right.
As to previous discussions on the mixer circuit (how it works) section, we know that the incoming signal is "beat against" another signal produced by the local oscillator (LO) circuit. By shifting the LO frequency, we can tune signals above and below the Amateur bands. First thing to do is locate the LO coils. In this picture, the LO coils are the ones with the screw adjustment on top. Notice the order of the labels is exactly opposite from the antenna input coils further back in the picture.
The LO is like any oscillator. Part of the circuit contains an LC (Inductance Capacitance) section.
In the CONAR, you can increase and decrease inductance a small amount by simply adjusting the screw adjustment, moving the coil slug up and down the coil form. For a large increase or decrease of Inductance, the coil form must be removed and a longer or shorter coil must be wound. This is a major pain and not very practical. It's far easier to change the frequency by adding or subtracting capacitance.
Here is a picture of the LO NPO (temperature compensated) disc capacitors behind the band switch. Notice a number of them have been paralled (added increase capacitance) to shift the LO's frequencies down so that the shortwave bands can be tuned. To decrease capcitance, solder a smaller capacitor to the ground side of the present capacitor's leads. Unhook the present capacitor's lead from the band switch and solder in the lead of the new smaller capacitor. This makes it easy to return everything back to normal whenever you wish.
Here is a picture showing the top of the CONAR receiver. Notice the large 2 section main variable capacitor in the center of the picture.
Because Amateur bands are limited, CONAR uses the smaller section of the two section tuning capacitor.
Notice the larger section is not hooked up at all. To greatly increase your tuning range to cover an entire shortwave broadcast band, unhook the smaller variable and attach a lead to the larger one. Tuning will be much narrower but a greater frequency range will be covered.
Notice I have not written which capacitor values to use. Part of the fun of the CONAR is experimentation. I leave it to the reader to go to his favorite electronic store or electronic junk box and grab a handful of disc caps and experiment to their heart's content. Because Broadcast shortwave stations can be found throughout the shortwave spectrum, its guranteed, the experimenter will pick up several no matter where the LO frequency happens to be.
Avoid the temptation to "tune" or "peak" the antenna input coils! Leave them tuned to the amateur bands. The Shortwave broadcast stations are so strong, that if you "peak out" the input coils, you will be constantly "riding shotgun" over the RF Gain control knob to prevent broadcast signals from overloading (and distorting the audio).
Have fun and remember: ALWAYS UNPLUG THE RECEIVER BEFORE WORKING ON IT !!!
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